This invention relates generally to the protection of an electrical power source from excessive transient voltages at the power terminal to which it is coupled.
Electrical transient pulses generated electromagnetically or by lightning strikes have heretofore been propagated from power outlet boxes to their power source with serious damage consequences from excessively high voltages. Protective circuitry for dealing with excessively high electrical voltages is generally well known as disclosed for example in U.S. Pat. Nos. 3,017,564, 3,683,234 and 4,539,617 to Barney, Rodewald and Delaney et al., respectively. The location of the protective circuitry between a power source and electrical loads is furthermore disclosed in the Barney and Delaney et al. patents. According to the Barney patent, a protective circuit is designed to protect a load from damage due to excessively high voltage under control of a load responsive relay. According to the Delaney et al. patent, transient pulse suppression on an AC power line is effected by a protective circuit between an AC load and a power line terminal involving a bidirectional diode arrangement to provide threshold shunting in association with low pass filtering.
It is an important object of the present invention to provide transient voltage suppressing circuitry adapted to be fitted into a power outlet box into which electrical loading is plugged in order to prevent damaging propagation of transient pulses from the power outlet box to the power source to which the box is coupled.